Patient interfaces, such as masks for covering the mouth and/or nose, are used for delivering gas to a patient. Such gases, like air, cleaned air, oxygen, or any modification of the latter, are submitted to the patient via the patient interface in a pressurized or unpressurized way.
For several chronic disorders and diseases, a long-term attachment of such a patient interface to a patient is necessary or at least advisable.
One non-limiting example for such a disease is obstructive sleep apnea or obstructive sleep apnea syndrome (OSA). OSA is usually caused by an obstruction of the upper airway. It is characterized by repetitive pauses in breathing during sleep and is usually associated with a reduction in blood oxygen saturation. These pauses in breathing, called apneas, typically last 20 to 40 seconds. The obstruction of the upper airway is usually caused by a reduced muscle tonus of the body that occurs during sleep. The human airway is composed of walls of soft tissue which can collapse and thereby obstruct breathing during sleep. Tongue tissue moves towards the back of the throat during sleep and thereby blocks the air passages. OSA is therefore commonly accompanied with snoring.
Different invasive and non-invasive treatments for OSA are known. One of the most powerful non-invasive treatments is the usage of Continuous Positive Airway Pressure (CPAP) or Bi-Positive Airway Pressure (BiPAP) in which a patient interface is connected to a pressure generator via a patient circuit including one or more tubes, wherein the pressure generator blows pressurized gas into the patient interface and into the patient's airway in order to keep it open. Positive air pressure is thus provided to a patient by means of the patient interface that is worn by the patient typically during sleep.
Examples for such patient interfaces are:
nasal masks, which fit over the nose and deliver gas through the nasal passages,
oral masks, which fit over the mouth and deliver gas through the mouth,
full-face masks, which fit over both the nose and the mouth and deliver gas to both, and
nasal pillows, which are regarded as patient interfaces as well within the scope of the present invention and which consist of small nasal inserts that deliver gas directly to the nasal passages.
The patient interface is usually positioned and donned to the patient's head using some kind of headgear. Further, the patient interface may comprise a forehead support. Such a forehead support is often designed as a pad that touches the forehead of a patient during use. It is often included in order to relief the pressure which the patient interface exerts onto the nose bridge.
Wearing a patient interface can be uncomfortable, since for providing an airtight seal between the patient interface and the patient's face, the patient interface has to be worn with a sufficient level of pressure on the face. It is thus evident that users of the patient interfaces experience a lot of disadvantages, wherein the most prominent disadvantage is the formation of facial red marks after a long-term usage of the patient interface. These red marks result from occlusions of blood vessels which arise from the pressure exerted by the patient interface.
A promising concept for preventing uncomfortable pressure points, red marks, indentations, and overall prolonged discomfort is the use of cushion elements that provide an alternating pressure onto the skin of the patient. This restores the skin blood flow in the depressurized part of the cushion element. One approach for providing cushion elements with an alternating pressure distribution is the use of electroactive polymers (EAPs) within the cushion elements. Dielectric elastomer actuators (DEAs) are smart material systems which produce large strains (up to 300%) and belong to the group of EAPs. Based on their simple working principle DEAs transform electric energy directly into mechanical work. DEAs are lightweight and free shapeable.
A DEA is a thin and flexible electroactive polymer sheet enclosed between two compliant electrodes. The thickness of the electroactive polymer sheet is controlled by the applied electrode voltage. Correspondingly, a thickness change results in elongation change. So both the thickness as well as the elongation of the sheet can be controlled. If applied to the skin, the alternating dimensions will impose an alternating pressure or stretch to the skin.
An example for a cushion element that includes EAP-actuators is known from WO 2013/183018 A1. The EAP-actuators used therein continuously alter the skin pressure distribution, provide a slow massaging motion to the skin, and relieve high local pressure peaks.
However, there is still room for improvement. One of the main technical challenges is the technical design and arrangement of such actuators within the cushion element. It is particularly challenging to design and arrange the actuators in such a way that static pressure points may be effectively avoided.
A typical way to produce an EAP actuator is to spin coat or blade the polymer layer and to spray coat or paint the compliant electrode. There is a need to segment the electrodes so that alternating pressure (switching from segment A to segment B) can be realized. However, these electrode-segments are placed at a certain distance away from each other in order to prevent electric arcing from one electrode to the other. The gap between the electrode-segments is usually in the range of 1-2 mm and minimally in the range of 200-500 μm. This gap can be responsible for static pressure points on the cushion element, which can lead to red marks.